Added tests.

(calling `Instances.set_reachable/1` only if instance had `unreachable_since`,
calling `Instances.set_unreachable/1` only if instance had nil `unreachable_since`).

This reverts merge request !733

that is the only change from nodeinfo 2.0 to 2.1

also this makes the nodeinfo tests use 2.1.json instead of 2.0.json

This reverts merge request !682

[#534] Made federation push sender be determined basing on content instead of `referer` header. Updated tests.

This is in preparation for 1.0. We'll be able to switch the config to the new
mechanism on PleromaFE then as well.

Closes #407

mastodon api: factor out status card fetching, move status card rendering to statusview, add opengraph extended data

Closes: pleroma/pleroma#557

Some previously issued stateless tokens have integer ids in them.